A cheery John Cardinal O’Connor was feeling blessed yesterday on his first day back at work — saying he hopes he’s strong enough to return every day.

“It’s a real joy to be here after 4½ months,” said O’Connor, who underwent brain surgery in the summer and has been weakened by subsequent radiation treatment.

“It’s wonderful. Thank God I’m back here,” said the 79-year-old cardinal as he entered New York Archdiocese headquarters at First Avenue and East 55th Street at 9:30 a.m.

“I feel strong. I hope I’ll be in each day,” he said before walking up a ramp and entering the building unaided.

O’Connor also took time to joke that “4½ months ago, I had a brain tumor removed. People will think I’m a lot smarter than I was back then.”

The cardinal, who has stumbled twice on altar steps at Mass recently, said the first thing he wanted to do was to get to his desk and “see how much it needs cleaning up. I have to get started all over again and get out there where the real people are.”

Before getting to work, he waved to well-wishers outside his office, saying, “Thanks a million.”

Later, O’Connor’s spokesman, Joseph Zwilling, said the cardinal reported having a good day after putting in nearly five hours of work, including meetings with Monsignor Edward O’Donnell, the archdiocese’s chancellor, and other staffers.

Zwilling said the cardinal will split time between keeping appointments at his residence at St. Patrick’s Cathedral and working at the office.

“He wants to get back into a routine of coming to the office on a regular basis,” Zwilling said.

O’Connor, who turns 80 on Jan. 15, has hinted he’ll retire soon. In any event, on his birthday, he will lose his voting power to elect a pope.

“That’s terrible,” he joked. “For 80 years, I never voted for a pope, and I don’t know if the pope voted for me.”

Pope John Paul II began serving as head of the church in 1978; O’Connor became a cardinal in 1985.